function utf8Decode(utftext) {
  let string = '';
  let i = 0;
  let c = 0;
  let c3 = 0;
  let c2 = 0;
  while (i < utftext.length) {
    c = utftext.charCodeAt(i);
    if (c < 128) {
      string += String.fromCharCode(c);
      i++;
    } else if (c > 191 && c < 224) {
      c2 = utftext.charCodeAt(i + 1);
      string += String.fromCharCode(((c & 31) << 6) | (c2 & 63));
      i += 2;
    } else {
      c2 = utftext.charCodeAt(i + 1);
      c3 = utftext.charCodeAt(i + 2);
      string += String.fromCharCode(((c & 15) << 12) | ((c2 & 63) << 6) | (c3 & 63));
      i += 3;
    }
  }
  return string;
}
const keyStr = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=';
export default {
  decode(input) {
    let output = '';
    let chr1,
      chr2,
      chr3;
    let enc1,
      enc2,
      enc3,
      enc4;
    let i = 0;
    input = input.replace(RegExp('[^A-Za-z0-9\\+\\/\\=]', 'g'), '');
    while (i < input.length) {
      enc1 = keyStr.indexOf(input.charAt(i++));
      enc2 = keyStr.indexOf(input.charAt(i++));
      enc3 = keyStr.indexOf(input.charAt(i++));
      enc4 = keyStr.indexOf(input.charAt(i++));

      chr1 = (enc1 << 2) | (enc2 >> 4);
      chr2 = ((enc2 & 15) << 4) | (enc3 >> 2);
      chr3 = ((enc3 & 3) << 6) | enc4;

      output += String.fromCharCode(chr1);
      if (enc3 !== 64) {
        output += String.fromCharCode(chr2);
      }
      if (enc4 !== 64) {
        output += String.fromCharCode(chr3);
      }
    }

    output = utf8Decode(output);

    return output;
  },
};
